Rebuilding Arch linux kernel

It turned out that every laptop I owned happened to need custom kernel
eventually. For instance, Acer
C720 had a less popular
light sensor, HP needed a specific version of WiFi driver etc. And this time,
Xiaomi Mi Notebook Air,
doesn’t work well with the kernels younger than 4.10, the touchpad becomes
unbearable jerky. Luckily there is an AUR package with LTS kernel
linux-lts49. Unfortunately,
it can’t be built in tmpfs because of limited size. But it turns out
that building minimal kernels is very easy in Arch linux indeed.

First, there is a service recording the names of kernel modules that were ever
loaded in the system:
modprobed-db. It also
allows interactive usage.

Second, one line needs be put into PKGBUILD:

make LSMOD=$HOME/.config/modprobed.db localmodconfig

This will configure the kernel build to only include specific needed modules.

The result is impressing:

The build finishes within 15 minutes (much less than I sent writing text)